They didn't create a real life light saber. They created a new particle that resembles the beam of a light saber. Keep in mind the particles where created by a large machine shooting a beam of protons into a vacuum chamber with a cloud of extremely cold rubidium atoms. That's a long way away from a handle sized stick producing those same particles and the particles stopping an a predefined length to make a sword.

I think the article did a pretty good job of explaining what is happening here. At least in terms that most people will understand. If they go into much more detail it quickly shoots over most people's head.